Machines, such as dragline excavators, mining shovels, hydraulic excavators, and the like, typically include two structures that are rotatable relative to one another. A rotating assembly is provided between the two rotatable structures to enable rotation between them. The loads acting on the rotating assembly may be unevenly distributed about a center of rotation, thereby resulting in points of stress concentration across the rotating assembly. This may result in points of peak loading which shift about the center of rotation as the structures rotate with respect to each other. The loads imposed on the rotating assembly, results result in uneven, constantly shifting weight distribution which may lead to damage of the rotating assembly.
U.S. Pat. No. 5,676,471 discloses an apparatus comprising a lower support structure having an upper surface, a circular lower rail which is mounted on the upper surface of the lower support structure and which is centered on a generally vertical axis. The apparatus further comprises the upper structure having a lower surface, a circular upper rail which is mounted on the lower surface of the upper structure and which is centered on the axis, a plurality of rollers which are located between the upper and lower rails and which support the upper structure for rotation relative to the lower structure about the axis. The rollers are rotatable about respective generally horizontal axis intersecting the vertical axis at a common point. Further, the apparatus includes one of the rails including an inwardly facing surface defining a portion of a sphere centered on the point, and each of the rollers including an outwardly facing surface which engages the inwardly facing surface and which defines a portion of a sphere centered on the point.